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by 1024MAK
23 Sep 2020 13:46
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 13059

Re: MTX 512 (debugging thread)

That’s very strange! So at power on, C11 is charging up (normal and too fast to see with a meter) and then slowly being discharged, and at a rate faster than R18 can recharge it. If C11 has already been changed, it’s unlikely but still possible that the replacement is faulty. Given the small voltage...
by 1024MAK
21 Sep 2020 19:00
Forum: HARDWARE
Topic: Rolling picture...sometimes
Replies: 3
Views: 137

Re: Rolling picture...sometimes

In answer to your other questions, yes the TMS9929A VDP produces all the video signals. The sync. signals are included in the composite monochrome video output (Y) on pin 36. A rolling picture normally is caused by either insufficient signal level / poor signal to noise ratio, or a problem with the ...
by 1024MAK
20 Sep 2020 11:36
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 13059

Re: MTX 512 (debugging thread)

There is one other possibility, and that is that there is an unwanted connection between another circuit and the reset circuit (either the track from J1/19 to R17, or the tracks between R17 and R18/C11/D13/R16 or the tracks between R16/R64/chip 9C {4079B} pin 1).

Mark
by 1024MAK
20 Sep 2020 11:06
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 13059

Re: MTX 512 (debugging thread)

The voltage across C11 should get very near the supply voltage (within 0.5V), certainly much higher than 3V. There is something dragging the voltage down, or rather something preventing it from climbing up. There are only three components that can cause this, the keyboard, C11 or the chip (9C, 4070B...
by 1024MAK
16 Sep 2020 10:10
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 13059

Re: MTX 512 (debugging thread)

A6C6AB17-42D3-47F3-8C3D-3346B8EF306D.jpeg Resistor R18 (10kΩ) should pull up the input (pin 1) of the 9C logic gate (4070B) to nearly 5V. R64 (820kΩ) is only there to provide a little bit of positive feedback from the output to the input to speed up the translation when switching between logic leve...
by 1024MAK
09 Sep 2020 13:55
Forum: GENERAL DISCUSSIONS
Topic: Guardian article ranking home computers
Replies: 1
Views: 340

Re: Guardian article ranking home computers

Yeah, that list is, well, not worth being called “The 20 greatest home computers – ranked!” because it’s not. I do agree with some of Geoff Boyd points. My take is: The experience in each country was different for a start. Not many Apples (if any) for sale in my part of England for example. Meanwhil...
by 1024MAK
30 Aug 2020 15:04
Forum: NEW HARDWARE
Topic: NFX Hardware description
Replies: 5
Views: 512

Re: NFX Hardware description

It’s only a draft. I’ve not added many decoupling capacitors or the 3.3V LDO voltage regulator yet.

Also it would be helpful if the pin-outs of the CF and the Wiznet be checked by someone who is actually awake please.

Mark
by 1024MAK
30 Aug 2020 14:56
Forum: NEW HARDWARE
Topic: NFX Hardware description
Replies: 5
Views: 512

Re: NFX Hardware description

NFX-Wiznet WIZ810SMJ draft schematic
NFX-Wiznet WIZ810SMJ draft schematic
NFX-Wiznet WIZ810SMJ draft.png (129.79 KiB) Viewed 497 times
Mark
by 1024MAK
29 Aug 2020 08:19
Forum: NEW HARDWARE
Topic: Memotech Network File Transfer
Replies: 15
Views: 756

Re: Memotech Network File Transfer

To me, it makes more sense if the MTX is the client. Firstly because normally the majority of the time the data flow will be from PC or website to MTX, and secondly, servers normally are the devices that have the large capacity mass storage media system(s). There are of course various ways of doing ...
by 1024MAK
22 Aug 2020 15:38
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 13059

Re: MTX 512 (debugging thread)

The TMS9928 and TMS9918 chips are designed for the American NTSC TV system. Only the TMS9929A can produce a 625 line, 50Hz PAL video signal. The TMS9129 can’t be used, as it’s designed for a different type of DRAM chip. So it’s address and data lines to the DRAM is different. Well, unless you make c...